In the related art, there is the on-demand type of inkjet printing system in which ink droplets are ejected from nozzles in an image pattern based upon an image signal, to form the image on a print media such as a paper sheet. The on-demand type of inkjet recording systems mainly consists of two subtypes: the heating element type and the piezoelectric element-type. For the configuration of the heating element type, as power is fed to a heating element in an ink-flow channel, a gas bubble is generated in the ink, and the gas bubble pushes the desired quantity of ink out from the nozzle. For the piezoelectric element-type, the piezoelectric element is energized to create waves in the ink to eject the desired quantity of the ink stored in the ink chamber out of the nozzle.
A piezoelectric element (piezo-element) is an element that converts a voltage to a force. When an electric field is applied to the piezoelectric element, stretching or shear deformation of the element takes place, causing a change in the volume of the ink chamber against which it is placed. A typical piezoelectric element is made of lead titanate zirconate.
In the configuration of an ink jet head using a piezoelectric element, a nozzle substrate is formed from a piezoelectric material. For this ink jet head, electrodes are formed on the two surfaces of the nozzle substrate to either side of the nozzle. The ink enters an area between the nozzle substrate and a substrate that supports the nozzle substrate. The ink forms a meniscus inside the nozzle and is held inside the nozzle. When a driving waveform is applied to the electrodes of the nozzle substrate to vibrate the piezoelectric element, the piezoelectric element around the nozzle vibrates. As the piezoelectric element vibrates, an ultrasonic wave vibration is generated inside the nozzle so that the ink in the meniscus is ejected. As the piezoelectric element on the nozzle substrate is energized to vibrate, vibration energy is concentrated from a peripheral edge portion of an ink droplet-ejection opening towards a center thereof so that the ink droplets are ejected from an ink surface in a perpendicular direction.
It is difficult to form plural nozzles with high precision and at low cost with respect to the piezoelectric element.